Haul rope or cable-driven railway transit systems have been in use for many years. U.S. Pat. Nos. 255,752, 332,934, 343,293, 404,498, 440,001, 466,880, 482,279, 511,596, 530,720, 536,611 and 546,955 include examples of such systems which were patented prior to 1900. In each case, a cable or haul rope was used as a traction member to draw a passenger or freight carrying vehicle along a transit path. Such systems have been widely used in many countries, as indicated by French Patent No. 701,740 and British Patent No. 14,208. More recent examples of transit systems employing a traction haul rope can be found in U.S. Pat. Nos. 3,797,407 and 4,092,929.
In the transit or transport systems above referred to, the vehicle or unit being propelled generally is supported on a track, rail or other support surface as it is being propelled by the traction member. It will be appreciated, however, that chair lifts, ski lifts, aerial tramways and similar systems also employ an elongated haul rope or traction member to propel a vehicle or passenger carrier unit along a path, usually without direct support of the vehicle on a track or rail. Typical of the chair lifts and aerial tramways in which a twisted wire haul rope is used as the traction member are the systems disclosed in my U.S. Pat. Nos. 4,462,314, 4,848,241 and 4,864,937, among others.
Considerable technology has been developed, therefore, in connection with driving, gripping, guiding, repairing, replacing and maintaining metallic haul ropes or traction members. Notwithstanding such effort over many years, there are still significant disadvantages which result from using a haul rope traction member in a transport, conveying or transit system. One problem which is commonly encountered is that it is difficult to apply power efficiently to a haul rope at locations other than the ends of the system. Torque transfer is a function of the rope tension, coefficient of friction and the angle of contact with the rope driving wheels. Thus, in most systems large, horizontal, vertical or inclined bull wheels are employed at opposite ends of a looped haul rope to drive the rope. Moreover, in order to create the necessary traction force, the tension on the haul rope must be very high to avoid slipping of the haul rope on the bull wheels. Attempts to add power intermediate the ends by small diameter sheaves have been made, but the torque transfer to the traction member, haul rope, is very inefficient because the contact is essentially a point contact, and wear on the small diameter drive sheaves is very high.
The use of large diameter bull wheels in turn makes it very difficult to advance or propel the vehicles or carrier units past, around or over the traction member drive unit. Funiculars cannot pass around such large bull wheels. In aerial tramways, the problem is often solved by detaching the passenger carrier unit from the haul rope at the ends. In non-detachable chair lifts and the like the passengers usually load and unload before the unit passes around the end bull wheels. In rail-based funicular systems the vehicles are often detached from the haul rope, the haul rope lifted from the drive assembly, or the system run as a shuttle between end terminals containing the drive assemblies.
Still another problem that can occur when driving or supporting rope-like traction members is that the sheave linear velocity cannot be matched to the rope linear velocity over the full contact height. Moreover, traction cable-based systems, even those employing rubber lined sheaves, induce a significant amount of vibration and noise as a result of the twisted strand haul ropes passing rapidly over the rolling support sheaves. Still further, the various couplings of the vehicle to the traction haul rope must be designed to pass over support sheaves, which further increases the system's complexity, as well as passing vibration and noise through to the vehicle or passenger carrier unit.
While considerable problems exist in connection with conventional traction member-based transit systems, they also afford substantial advantages. The traction member can insure very positive control of the position and velocity of the vehicle being propelled over the transit path. Such traction-based systems are well suited for automated or driverless transport of passengers and freight, and they eliminate the necessity of having vehicles with independent on-board power systems. They are adaptable to a wide variety of applications and inherently can provide relatively low cost systems to install and maintain.
While many efforts have been directed to gripping, guiding and driving elongated traction elements, little effort has been directed toward the traction member itself. The primary technological advances in connection with traction members have been directed toward improving the tensile strength of the haul ropes. While significant, it is also highly desirable in terms of safety and structural costs to employ traction members which are not under high tensile loading forces. The solution to improving traction member-based transit systems, therefore, does not appear to ultimately reside in merely increasing the traction member's strength and/or size.